In recent years, a special type of satellite system has been widely used which involves direct communications between satellites and small, low-cost terminal stations, sometimes referred to as VSAT's (very-small-aperture terminals). These VSAT ground stations operate with antenna apertures of about 1 meter or less.
The proper choice of an accessing format to accommodate a complete network of VSATs over a particular satellite bandwidth requires careful selection and design of transmitters, satellite, and receivers. To attain this goal and, in particular, to directly carry information to and from a home base via synchronous orbit satellites, a concept of a VSAT network using a common hub station designed to be a large earth terminal has been proposed. Techniques used for telecommunications of this type are commonly referred to as direct broadcasting by satellite (DBS).
Generally, an up-link forward transmitting hub station in DBS is used for broadcasting data, video, or voice in either digital or analog form to many VSATs. Techniques for return-link transmission from VSATs back to the hub station either use a separate return link transponder or share the transponder with the forward-link transmission. When the forward broadcast link fills the transponder, sharing by return links requires these links to use what is called spread spectrum (SS) techniques where the average energy of the return-link transmitted signal is spread over a bandwidth which is much wider than the information bandwidth. Using SS transmission in the same transponder as the forward link conserves space segment resources. However, transmitted power levels must be very low in order to minimize interference to the forward link, and as a result, SS techniques results in very limited capacity of each link, so information bit rates on the return links tend to be low (about 100 bit/sec).
In view of the foregoing, it is apparent that there is a need for an improved technique for same-transponder return-link signal transmission in DBS networks.